Conceptual Physics

http://science.hq.nasa.gov/kids/imagers/ems/ems.html

http://imagine.gsfc.nasa.gov/docs/introduction/emspectrum.html

http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/radiation/the_electromagnetic_spectrumact.shtml